The goal of this project is to understand how specification and patterning of internal organs is accomplished during vertebrate embryogenesis, with a particular focus on the origins of the vascular and hematopoietic components of the circulatory system. We have previously characterized a number of zebrafish mutants that cause specific defects in the early development of either blood vessels or blood cells. We have also developed new experimental techniques for studying circulatory development in zebrafish embryos, including embryonic blood cell transfusion and 3-D confocal microangiography. Using these and other genetic and experimental tools we are attempting to (1) elucidate the embryonic origins of vascular endothelial cells and hematopoietic stem cells and determine how these two lineages are related, and (2) understand how the patterning of the developing vasculature is directed. We have already been able to show that single gene defects such as the gridlock mutation can cause defined, localized defects in the patterning of blood vessels. We are now trying to further define the nature and consequences of gridlock and other potential vascular patterning mutations using a variety of genetic, experimental embryologic, molecular, and molecular genetic methods. We are also studying dorsoventral specification and patterning of the major axial trunk vessels (axial artery or aorta and axial vein. We have obtained evidence supporting a "two-signal model" for axial vessel formation reminiscent of that invoked to explain the dorsoventral patterning of the neural tube, and we are working to understand the nature and activities of these signals. We are also further studying hematopoietic-specific mutations, with emphasis on several early-acting mutations which may cause defects in the formation of hematopoietic progenitor cells.